1. Field of the Invention
This invention relates to re-sequencing and retransmission entities at a network node, and more specifically to efficient interlayer control between re-sequencing and retransmission entities at a network node.
2. Discussion of the Related Art
Mobile devices such as mobile phones, Personal Digital Assistants (PDAs), laptop computers, etc. are becoming increasingly more popular. 3G (Third Generation Mobile System) is a generic name for a set of mobile technologies which use a host of high-tech infrastructure networks, handsets, base stations, switches and other equipment to allow mobile devices to offer high speed Internet access, data, video, and CD-quality music services. Most 3G services are related to technologies based on Code Division Multiple Access (CDMA). CDMA is a digital wireless technology that allows multiple users to share radio frequencies at the same time without interfering with each other. CDMA2000 is one new high-speed version of CDMA that is used by 3G services.
1×EV-DV is one variant of the CDMA2000 3G standard. 1×EV-DV is a variant and an evolution of the cdma2000 1× radio transmission technology (1× RTT) that includes systems optimized for packet data services, with a flexible architecture based on internet protocol (IP) protocols, and that can be embedded in handsets, laptops, notebooks and other fixed, portable and mobile devices.
Radio Link Protocol (RLP) is a link layer protocol used with a CDMA2000 traffic channel to support CDMA data services. It has retransmission and re-sequencing procedures to reduce the frame error rate (FER) exhibited by CDMA traffic channel. RLP is a pure NAK-based protocol in data transfer.
Hybrid Automatic Retransmission Request (HARQ) is a link-adaptation technique that is employed by 1×EV-DV. HARQ employs multiple instances of an acknowledgment-based stop-and-wait ARQ protocol. Each instance is termed as a phase. HARQ also uses combining techniques on the original and retransmitted packets to improve the retransmission operation. The combining techniques can be soft combining such as Chase combining or incremental redundancy (IR). Some HARQ variables include: (1) NARQP, the total number of HARQ phases; (2) MAXRETRANS, the maximum number of HARQ retries before the RF frame is abandoned; and (3) Al, the instance of HARQ phases.
Employing HARQ in 1×EV-DV, link layer receivers (e.g., RLP) may no longer need to carry out the retransmission request for missing data frames since retransmission using HARQ procedures provides satisfactory residual frame error rate for data services. A re-sequencing function still needs to be performed above HARQ whether by RLP or another entity. Frames buffered after the missing frame can only be passed on to the upper layer when the physical layer retransmission of the missing frame is abandoned by the HARQ.
Synchronous HARQ imposes a constraint that all frames are delivered in a fixed order of multiple HARQ instances (or phases), i.e., the frames are sent over HARQ phases 1, 2, 3, 4, 1, 2, 3, 4, . . . , etc., if the total HARQ phase is 4. Therefore, the delay and sequence of frame delivery is somewhat predictable.
Currently, re-sequencing entities rely on a timer-based scheme to determine when to quit waiting for the missing frame for sequential delivery to the upper layer. In timer-based schemes, a timer is started whenever a missing data frame is detected. The maximum waiting time to “give up” the missing frame is between when the frame is declared missing and when a new frame is received from the same HARQ instance (or phase). Therefore, the maximum waiting time is composed of two portions: (1) the time between when the frame was NAKed in the physical layer for the first time and the time the same missing frame is was actually detected by the link layer at the receiver, i.e., Tmiss—frame, (2) the time required for HARQ to exhaustedly retransmit the missing frame, i.e., NARQP×MAXRETRANS. The time, Tmiss—frame, consists of at least the following required time: (1) a frame inter-arrival time to the transmitter between the missing frame and the next received frame, which facilitates the detection of the missing frame at the re-sequencing entity; and (2) a base station scheduling delay. This latter delay (2) occurs since with multiple data instances, the new frame, which will facilitate the detection of the missing frame, is not necessarily sent immediately after the missing frame depending on transmission priority.
1×EV-DV also employs asynchronous HARQ where the data is sent with accompanying phase information, Al, (possibly out of sequence) indicated in the control channel. In this case, the timer-based scheme can no longer work since the transmitter is not following a phase sequence order and timing cannot be predicted as to when exactly the abandonment will happen. Packets may be sent based on priority, and not on sequence number.
Current solutions for both synchronous and asynchronous HARQ are problematic since when a packet is missing, the physical layer may request retransmission and a link layer (e.g., RLP) does not know how long to wait before sending a NAK. Further, a transmission side may send a missing frame twice due to a retransmission request from the HARQ and a NAK from the link level. Moreover, a re-sequencing problem exists since the link layer may be receiving frames out of sequence (asynchronous HARQ) or out of sequence due to missing frames (synchronous HARQ). These situations also cause a further problem in that they require a link layer to have an increased buffer requirement.
Therefore, an inter-layer control scheme between retransmission and re-sequencing entities is needed that eliminates the delay and re-sequencing problems and allows reduced buffer requirement at the link layer.